over Russia's objectives, suggesting instead that the strikes were aimed at Western-backed rebels who've fought both the IS and forces from Syrian President Bashar al-Assad.

Kerry said he and his Russian counterpart, Sergei Lavrov, could meet as early as Thursday.

"We agreed on the imperative of, as soon as possible - perhaps even as soon as tomorrow, but as soon as possible - having a military-to-military de-confliction discussion," Kerry said during a joint appearance with Lavrov.

The Russian attacks occured before both Washington and Moscow could talk on how to avert clashes between different militaries.

Moscow says its strikes on Wednesday hit eight Islamic State targets. But the head of Syria's opposition group says one bombing run in Homs killed 36 civilians.

"The Russians struck northern Homs today and killed 36 innocent people...who fought against extremism," said Khaled Khoja, head of the National Coalition, a coalition of Syrian opposition groups.

"Russia is intervening not to fight ISIL, but to prolong the life of Assad and support the continuous killing on a daily basis of civilians," Khoja said, using an acronym for Islamic State.